2-benzimidazalyldithio carbamates

ABSTRACT

Heterocyclic esters of dithiocarbamic acid wherein the heterocycle is 2-imidazolyl, 2-imidazolinyl, 2-benzimidazolyl, or substituted derivatives thereof which esters are useful for accelerating the vulcanization of rubber.

{limited States ?atent DAmico Apr. 19, 1973 [54] Z-BENZIMIDAZALYLDITHIO [56] References Cited CARBAMATES UNITED STATES PATENTS [75] Inventor; John Joseph DAn'lico, Akron, Ohio 3,361,752 1/1963 DAmico ..260/309.2

[73] Assignee: Monsanto Company, St. Louis, Mo. OTHER PUBLICATIONS 22 Filed; 2, 1970 John J. DAmico Chemical Abstracts, Vol. 67, page 5082 (1967) [21] Appl. No.: 86,348

Related Us. Application Data Primary Examiner-Alex Mazel Assistant Examiner-Jose Tovar 2 22 638,595, y 15, 1967, Attorney-Richard 0. Zerbe and F. M. Murdock [57] ABSTRACT [52] US. Cl....'.260/247.1, 260/2565 R, 260/293.57,

260/309, 260/3092 260/3095, 260/784 Heterocyclic esters of dithiocarbamic acid wherein the 51 Int. Cl. ..C07d 87/46 heterocycle is 2-imidazolyl. m y [58] Field of Search ...'....260/309.2, 247.1, benzimidazolyl, or s st tut d derivatives thereof 260/291 57 which esters are useful for accelerating the vulcanization of rubber.

9 Ciaims, No Drawings 2-BENZIMIDAZALYLDITHIO CARBAMATES This application is a division of application Ser. No. 638,595, filed May 15, 1967 now U.S. Pat. No. 3,565,894, February 23, 1971.

The present invention relates to a new class of products, namely, meta dinitrogen heterocycle esters of dithiocarbamic acids, and to their use for accelerating the vulcanization of rubber.

Salts of dithiocarbamic acids have achieved wide acceptance for accelerating vulcanization of sulfur-vulcanizable rubbers, but esters have been heretofore much less effective. The meta dinitrogen heterocycle esters, however, are potent accelerators.

The new compounds may be represented by the formula where Z is a heterocycle, the ring members of which consist of three or four carbon atoms and two meta nitrogen atoms, which heterocycle is attached to sulfur at the carbon between the nitrogen atom. One of the bonds between said intermediate carbon atom and the two nitrogen atoms is unsaturated. Substituents may be present on one or more of the other carbon atoms. More particularly, Z is unsubstituted Z-pyrimidinyl, 2- pyrimidinyl containing one or more substituents, unsubstituted dihydro-2-pyrimidinyl, dihydro-Z-pyrimidinyl containing one or more substituents, unsubstituted tetrahydro-Z-pyrimidinyl, tetrahydro-Z-pyrimidinyl containing one or more substituents, unsubstituted 2- imidazolyl, Z-imidazolyl containing one or more substituents, unsubstituted 2-imidazolinyl, or 2-imidazolinyl containing one or more substituents. The substituents may comprise lower alkyl, aralkyl; e.g., benzyl, alicyclic, or aryl. The

group is the residue of a thiocarbamyl radical.

The new compounds can be prepared by the alkaline condensation of a thiocarbamyl halide with ZSH, where Z is a heterocycle as defined. The following are typical examples of suitable mercaptans:

' Z-mercaptoimidazole 2-mercapto-4,5dimethylimidazole Z-mercaptoimidazoline ,5dimethyl-Z-mercapto-3-phenyll imidazoline 2-mercapto-lphenyl-2-imidazoline Z-mercapto-benzimidazole 4-methyl-2mercaptoimidazoline 2-mercapto-3 ,4 ,5 ,6-tetrahydropyrim idine 2-mercapto-5-methyl-3,4,5,6-tetrahydropyrimidine 2-mercapto-3isopropyl-4,6,6-trimethyldihydropyrimidine 2-mercapto-3 cyclohexyl-4,6,6-tri methyldihydropyrimidine 2-mercapto-S-alphanaphthyl-4,6,6-trimethyldihydropyrimidine Z-mercapto-3-phenyl-4,6,6-trimethyldihydropyrimidine 2-mercapto-3-o-tolyl-4,6,6-trimethylv dihydropyrimidine 2-mercapto-4,6,6-trimethyl-dihydropyrimidine 2-mercapto-4,4,6-trimethyl-dihydropyrimidine 2-mercapto-4-ethyl-3,4,5,6-tetrahydropyrimidine 2-mercapto-4,4-diethyl-3 ,4,5 ,6-

tetrahydropyrimidine 2-mercapto-5-methyl-3,4,5,6-tetrahydropyrimidine 2-mercapto-5,5-dibutyl-3,4,5,6-

tetrahydropyrimidine 2-mercapto-4-alphanaphthyl-3,4,5,6-

tetrahydropyrimidine 2-mercapto-3,4,5,6-tetrahydropyrimidine Z-mercaptopyrimidine.

In the case of pyrimidinyl mercaptans, 2-mercapto- 4,6-dimethylpyrimidine is readily obtained from existing raw materials and yields especially effective accelerators. The hydrochloride of 2-mercapto-4,6- dimethylpyrimidine is a commercially available intermediate which will be hereinafter designated hydrochloride intermediate. The 4,6-dimethiyl-mercaptopyrimidine base is conveniently formed in situ by addition of alkali and condensed with the desired thiocarbamyl halide. The chlorides are usually satisfactory, but bromides and iodides can be used. The amino substituent of the thiocarbamyl halide is preferably secondary amino. In

x and y independently can be lower alkyl, for example methyl, ethyl, propyl, butyl, or amyl; lower alkenyl, for example allyl or methallyl; lower alkenyl substituted by halogen, for example 2-chloroallyl or 2-bromoallyl; alicyclic, for example cyclopentyl or cyclohexyl; aralkyl, for example benzyl or phenethyl; aryl, for example phenyl, tolyl, or naphthyl; or taken together with the nitrogen form a heterocycle of four to eight carbon atoms, for example pyrrolidinyl, piperidino, Z-methyl- 5-ethylpiperidino, hexamethylenimino, morpholino, 2,6-dimethylmorpholino, 2,S-dimethylpyrrolidinyl, heptamethylenimino, and octamethylenimino.

The following examples illustrate the preparation of the new compounds but are not to be taken as limitative.

The example following illustrates the preparation of a meta dinitrogen heterocycle ester in which the heterocycle contains three carbon atoms in the ring and one phenyl substituent outside the ring.

EXAMPLE 1 The 5 ,5 dimethyl-Z-mercapto-3-phenyll imidazoline required for this example was obtained by adding 60.8 grams (0.6 mole) of carbon bisulfide in one portion to a stirred solution of 49.3 grams (0.3 mole) of N-(2-amino-2-methyl)propyl aniline, ml. of ethyl alcohol, and two drops of piperidine. The mixture was heated at refluxing temperature (4768C.) for 24 hours, cooled to 0C., and then stirred at 0-l0 C. for an hour. After filtering, the product was airdried at 2530C. giving a white solid, M.P. l7ll72 C. in 86.5 percent yield. Upon recrystallization from alcohol, the MP. was unchanged. The product analyzed 13.43 percent nitrogen and 15.57 percent sulfur compared to 13.58 percent nitrogen and 15.54 percent sulfur calculated for C H N S. Although the product is named on the basis of the mercaptan form, it is probably in the tautomeric thione form. However, reaction in alkaline medium apparently involves the sulfur.

To a stirred solution comprising 20.7 grams (0.1 mole) of the 5,5-dimethyl-2-mercapto-3-phenyl-limidazoline so prepared, 6.6 grams (0.1 mole) of 85 percent potassium hydroxide, 300 ml. of acetone, and 20 ml. of water was added in one portion 15.2 grams (0.1 mole) of diethylthiocarbamyl chloride. The mix-,

ture was stirred for 18 hours at 25-30C. whereupon there was added 500 ml. of ethyl ether and 500 ml. of water. After stirring for 15 minutes, the separated ether solution was washed with water until neutral and dried over sodium sulfate. The ether was removed in vacuo at a maximum temperature of 8090C./ 1-2 mm. 5,5- Dimethyl-3-phenyl-2-imidazolinyl diethyldithiocarbamate was obtained as a viscous amber liquid in 81.5 percent yield. Analysis gave 12.16 percent nitrogen and 19.17 percent sulfur compared to 13.07 percent nitrogen and 19.95 percent sulfur calculated for l6 23 3 2- The product of Example 1 was employed as the accelerator in a composition comprising:

Parts by Weight Smoked sheets rubber 100 Carbon black 50 Zinc oxide Stearic acid 3 Saturated hydrocarbon softener 3 Antioxidant 2 Sulfur 2 5,5-Dimethyl-3-phenyl-2-imidazolinyl diethyldithiocarbamate 0.5

vulcanization was completed in 30 minutes at a temperature of 144C. The following results were obtained:

Modulus 2050 lbs/in Tensile 3900 lbsJin Mooney Scorch at 135C. 5.5 minutes The following examples illustrate the preparation of meta dinitrogen heterocycle esters in which the heterocycle contains three carbon atoms in the ring, two of which are also part of a benzene ring.

EXAMPLE 2 To a stirred solution comprising 37.6 grams (0.25 mole) of Z-mercaptobenzimidazole, 40 grams (0.25 mole) of 25 percent sodium hydroxide, and 250 grams of water was added, in one portion, 38 grams (0.25 mole) of diethylthiocarbamyl chloride and the mixture stirred for 4 hours. The precipitate was filtered, washed with water until neutral and air-dried. 2-Benzimidazolyl diethyldithiocarbamate was obtained in 89 percent yield as a cream solid. After recrystallization from ethyl alcohol it melted at 169-171C. Analysisgave 15.84 percent nitrogen and 23.95 percent sulfur compared to 15.83 percent nitrogen and 24.16 percent sulfur calculated for C I-1 N 8 EXAMPLE 3 To a stirred solution comprising 30 grams (0.2 mole) of Z-mercaptobenzimidazole, ml. of benzene and 30 ml. of triethylamine was added, in one portion, 35.5 grams (0.2 mole) of diisopropylthiocarbamyl chloride. The mixture was stirred for hours, cooled, and the solid collected by filtration. The 2-benzimidazolyl diisopropyldithiocarbamate thus obtained was slurried with hot methanol and the product filtered from solution. The white solid softened at 152C. and decomposed above C. Analysis gave 14.1 percent nitrogen and 21.22 percent sulfur compared to 14.32

percent nitrogen and 21.85 percent sulfur calculated for C H N S EXAMPLE 4 Substituting an equimolar amount of morpholinothiocarbonyl chloride for the diisopropylthiocarbamyl chloride in Example 3, 2- benzimidazolyl-4-morpho1inocarbodithioate was obtained as a pale yellow powder. After slurrying with methanol and filtering, the residue was a white solid melting at 21722lC. Analysis gave 14.92 percent nitrogen and 22.74 percent sulfur compared to 15.05

percent nitrogen and 22.96 percent sulfur calculated for C H N OS EXAMPLE 5 Substituting an equimolar amount of dibutylthiocarbamyl chloride for the diisopropylthiocarbamyl chloride in Example 3, the product was extracted with ether, the ether layer separated, washed three times with water, and filtered. The filtrate was evaporated to half its volume, slurried in heptane and water, and filtered. 2-Benzimidazolyl dibutyldithiocarbamate was obtained as a white solid melting at 127-129C. Analysis gave 13.57 percent nitrogen and 19.84 percent sulfur compared to 13.07 percent nitrogen and 19.95 percent sulfur calculated for C I-1 N 8 EXAMPLE 6 A solution was prepared by mixing 30 grams (0.2 mole) of Z-mercaptobenzimidazole, 13.2 grams (0.2 mole) 85 percent potassium hydroxide, 600 ml. of acetone, and 10 ml. of water, heating to 55C. and, with stirring, maintaining the temperature at 5556C. for 30 minutes. The solution was then cooled to 25C. and to it was added in one portion, with stirring, 35.6 grams (0.2 mole) of hexamethyleniminothiocarbonyl chloride. The reaction mixture was stirred at 2530C. for 24 hours, then added to 2,000 grams of ice water, and stirred at 0-10C. for 30 minutes. The precipitate was collected by filtration, washed with water until neutral, and air-dried at 2530C. 2-Benzimidazolyl hexahydro-l H-azepine- 1 -carbodithioate was obtained in 80.7 percent yield as a light brown solid. Analysis gave 14.36 percent nitrogen and 22.48 percent sulfur compared to 14.42 percent nitrogen and 22.00 percent sulfur calculated for C I-1 N 8 It melted at 190-191 C. after recrystallization from alcohol.

EXAMPLE 7 To a stirred solution comprising 15 grams (0.1 mole) of Z-mercaptobenzimidazole, 6.6 grams (0.1 mole) of 85 percent potassium hydroxide, 300ml. of acetone, and ml. of water was added, in one portion, 12.4 grams (0.1 mole) of dimethylthiocarbamyl chloride. The mixture was then heated at 5060C. for 5 hours, cooled to 25C., and added to 1,000 grams of ice water. After stirring for one-half hour, the precipitate was collected by filtration, washed with water until neutral to litmus, and air-dried at room temperature. 2- Benzimidazolyl dimethyldithiocarbamate was obtained in 80 percent yield as a tan solid. After recrystallization from ethyl alcohol it melted at 193l95C. Analysis gave 18.04 percent nitrogen compared to 17.71 percent calculated for C ,,H N S EXAMPLE 8 Substituting an equimolar amount of dipropylthiocarbamyl chloride for the dimethylthiocarbamyl chloride in Example 7, the mixture was heated at 5060C. for 5 hours, added. to 1,000 grams of ice water, and isolated as in Example 7. 2-Benzimidazolyl dipropyldithiocarbamate was obtained as a yellow solid in 82 percent yield. After recrystallization from ethyl acetate it melted at 125-126C. Analysis gave 14.35 percent nitrogen and 21.60 percent sulfur compared to 14.32 percent nitrogen and 21.85 percent sulfur calculated for C l-l N S EXAMPLE 9 To a stirred solution comprising grams (0.1 mole) of 2-mercaptobenzimidazole, 6.6 grams (0.1 mole) of 85 percent potassium hydroxide, 150 ml. of acetone, and 5 grams of water was added, in one portion, grams (0.1 mole) of ethylthiocarbaniloyl chloride and the mixture heated at 50.60C. for 5 hours. After cooling to 5C., 400 ml. of water and 50 ml. of ethyl ether were added and stirring continued at 5l0C. for 30 minutes. The precipitate was collected by filtration, washed with water until neutral to litmus, and air-dried at -30C. 2-Benzimidazolyl N-ethyldithiocarbanilate was obtained in 92.5 percent yield as a tan solid.

After recrystallization from ethyl alcohol it melted at 191-193C. Analysis gave 12.34 percent nitrogen compared to 13.41 percent calculated for C I-1 N 8 EXAMPLE 10 To a stirred solution comprising 37.5 grams (0.25 mole) of Z-mercaptobenzimidazole, 16.5 grams (0.25 mole) 85 percent potassium hydroxide, 300 ml. of acetone, and 10 ml. of water was added, in one portion, 43.9 grams (0.25 mole) of methylthiocarbaniloyl chloride and the mixture heated at 50-60C. for 5 hours. After cooling to 5C. 500 ml.of cold water were added and stirring continued at 5l0C. for minutes. The precipitate was collected byfiltration, washed with water until neutral to litmus, and airdried at .25 3 0C. 2-Benzimidazolyl N-meth'yldithiocarbanilate was obtained in 80 percent yield as a tan solid. After recrystallization from ethyl alcohol it melted at 229-230C. Analysis gave 13.83 percent nitrogen and 21.41 percent sulfur compared to 14.04 percent nitrogen and 21.42 percent sulfur calculated for C15H13N3S2- Employing substantially the same reaction conditions and replacing the methylthiocarbaniloyl chloride with an equimolar amount, respectively, of l-pyrrolidinylthiocarbonyl chloride and 1-piperidinylthiocarbonyl chloride, further examples were prepared possessing the following physical properties:

EXAMPLE 1 l 2-Benzimidazolyl l-pyrrolidinecarbodithioate, a tan solid, M.P. 203-205C. after recrystallization from ethyl alcohol, in 80.7 percent yield. Analysis gave 15.88 percent nitrogen and 24.40 percent sulfur compared to 15.96 percent nitrogen and 24.35 percent sulfur calculated for c, H,,N,s,.

EXAMPLE l2 2-Benzimidazolyl l-piperidinecarbodithioate, a tan solid, M.P. l98-200C., after recrystallization from alcohol/chloroform, in 83.5 percent yield. Analysis gave 14.70 percent nitrogen and 22.85 percent sulfur compared to 15.15 percent nitrogen and 23.11 percent sulfur calculated for C T-1 N 8 The data in the tables below illustrate useful properties for accelerating vulcanization of rubber. A typical natural rubber tread stock was compounded compris- Parts by Wei ht Smoked sheets rubber 1%)0 Carbon black 7 Zinc oxide 5 Stearic acid 3 Saturated hydrocarbon softener 3 Antioxidant 1.5 Sulfur 2.5

To each of several portions of the base stock was added 0.5 part by weight of accelerator as indicated below:

Stock Accelerator AA 2-BenzimidazolylN-methyldithio carbanilate BB 2-BenzimidazolylN-ethyldithio carbanilate CC Z-Benzimidazolyl l-pyrrolidine carbodithioate DD 2-Benzimidazolyll-piperidine carbodithioate vulcanization was completed at a temperature of 144C. The modulus and tensile properties of the 15- minute cures and Mooney scorch are recorded in Table TABLE 1 Stock Modulus Tensile Mooney Scorch AA 1420 3800 10.2 BB 1430 3950 8 .8 CC 2000 4200 8.0 DD 1800 3800 8.1

In the following test the rubber compositions con tained a retarder of vulcanization. A stock was compounded comprising:

N-Nitrosodiphenylamine To the above therewas added in separate stocks 0.5

- part of accelerator asfollows:

Stock vulcanization was completed at a temperature of 144C. The modulus and tensile properties and Mooney scorch are recorded in Table ll.

TABLE II Cure time 1 Mooney Stock in minutes Modulus Tensile Scorch BE 15. 1850 4100 -15 r y "950 2380 j 30 qHOO .3370 714 45 1670 3440 3 n 60 1670 3190' 'GG l5 1010 2630 8.4 '30 1400 3020, y

45 1540 a 3090,. V so; 1540 3130v HH 15'. 1 900 3710 v v 'Butadiene-styrene copolymer rubberwas blcndedin' a standard'formula'as follows:

' Carbon black 50.

Zinc oxide 4 Stearic acid 2 .Satursted hydrocarbon softener l Antioxidant l .5 Sulfur 1.75

- To each, of several portions of thc base stock was added 1.2 parts weight of accelerator as indicated below:

Accelerator u Z-Benzintidszolyl diethyldithio carbsmate' 5 Z-Benzimidssolyl l-pyrrolidine c'srbodithioste Stock :1 v v in: r o

Vulcanization was completed at a temperature of l44C. The modulus and tensile properties of the 60- The product'of Example 6 was employed as the accelerator. in a composition comprising:

Pm by g; Smoked sheets rubber I 'Csrbonblsc'k 50 Zinc oxide 5 Stesric scid 3 Saturated hydrocarbon softener Y 3 Sulfur Y 2.5

a Z-Benzimidaholyl hexshydro-iH-azypinel-csrbodithio'ate 0.5

J has given good results in the'following corripositionfj' Q 8 j vulcanization was completed in 30 minutes at a tem-' perature of 144C; and the following results were obtained:

2550 lbs/in ,7 3300lbs./in' 10.3 minutes Modulus Tensile Mooney scorch at 'C.

The accelerator dosage will usuallyfall within the range of 0.1-5.0 parts accelerator per 100 parts by weight of rubber. As mentioned above the new compounds are useful for accelerating the vulcanization of EPDM rubber, and in this and other rubbers of low unsaturation the accelerator dosage will usually be higher than for natural rubber. Moreover, it may be expedient.

to use. the new compounds in conjunction with'a secon dary accelerator,. as for tobenzothiazole. i

The American Society for Testing Materials (ASTM) defines EPDM in the 1965 Book of ASTM I Standards, part 28, page 695; as follows: EPDM- T" polymer containing ethylene. and propylene in the a backbone and a diene in the side chai'r'n Amberg discusses {the dienes--- which have been ,use'd 1 with I ethylene and propylene in VulcanizatiohpfElastoinehi,

- 324, 325 (Alliger and. Sjothum ed. l 963).-Am berg-- states: .Good results have been obtainedwith compounds which have one internal and one terminal double bond, Dicyclopentadiene'is one of the preferred dienes. Z-Me'thylene-norbornene' and ll -ethylehll'k tridecadienej are examples of other monomers which react. satisfactorily."- Cyclooctadiene and 51,4-hejir- 1 adiene are also usedas the diene monomer of EPDM; The addition of 1.5 parts by weight 'of'oneiof the new accelerators followed curing for lofrninut'es at 7 C;

. jz' ereaptobenaothiazole I 1 it is intended to cover all engages and' modifica tions of the examples of the :inventionherein chosen for purposes of disclosure which donotconstitute departures from the spirit and scopeof the inventions 1 I'Whatisclaimedis: .1'.Acompound ofthe'fomula I where randy independently are -alky l:

carbon" atoms, allyL- methallyl, fZ-Chlo'roallyl, 2- bromoallyl, cyclopentyl, cyclohexyl, i'phenyly tolyl," naphth'yl, benzyl or phenethyl and taken "together with the nitrogen are pyrrolidino, piperidino, Z-methyI-S ethyl piperidino, l'ieiramethylenimino, morpholino, 2,6- I dimethylmorpholino, 2,5'dirnethylpyrrolidino;j- .heptamethylenimino and octameth'ylenimino; and Z is 2 benzimidazolyl.

2. A compound or claim 1 wherein): and are alkyl. 3. A compound of claim l wherein' a and yare taken together. a

example Z-mercap- 9 m 4. A compound of claim 1 wherein x is alkyl and y is is morpholino. phenyl. 8. A compound of claim 1 wherein 5. A compound of claim 1 wherein x and y are ethyl. 6. A compound of claim 1 wherein x y is piperidino.

l0 9. A compound of claim 1 wherein is pyrrolidino.

7. A compound of claim 1 wherein X 3 is hexamethylenimino. 

2. A compound of claim 1 wherein x and y are alkyl.
 3. A compound of claim 1 wherein x and y are taken together.
 4. A compound of claim 1 wherein x is alkyl and y is phenyl.
 5. A compound of claim 1 wherein x and y are ethyl.
 6. A compound of claim 1 wherein is pyrrolidino.
 7. A compound of claim 1 wherein is morpholino.
 8. A compound of claim 1 wherein is piperidino.
 9. A compound of claim 1 wherein is hexamethylenimino. 